The present invention is concerned with an acceleration pump of a carburetor adapted for use in an internal combustion engine and, more particularly, with an acceleration pump capable of accurately controlling the rate of supply of acceleration fuel in response to the change in the temperature of the engine.
In order to reduce the amount of combustible unburnt substance in the exhaust gas, as well as to decrease the fuel consumption, it has been proposed to reduce the rate of supply of acceleration fuel specifically when the engine temperature is high. To this end, temperature detection is performed making use of suitable temperature detecting means such as a bimetal, temperature-sensitive element including wax and like means.
However, the use of bimetal has been found inappropriate, because the acceleration pump requires, as is well known, a considerably large actuating force. More specifically, the bimetal itself is deflected when the pressure of the acceleration fuel provided by the acceleration pump is applied thereto, so that it cannot perform the correct adjustment of the acceleration fuel supply in accordance with the change in the engine temperature. Generally speaking, a larger amount of acceleration fuel is delivered than the optimum amount for the detected temperature, when the acceleration pump is combined with the bimetal.
For this reason, it is preferable to use an incompressible temperature detecting element for correctly controlling the acceleration fuel in relation with the engine temperature. However, the temperature detecting element has not been used so as to control the stroke of the piston of the acceleration pump, because trouble raises as follows.
In acceleration pump combined with the incompressible temperature detecting element, the arrangement is such that the incompressible temperature detecting element actuates a stopper member which is housed by a cylinder and adapted to be moved in the stroking direction of a piston which is housed also by the cylinder.
Generally speaking, the incompressible temperature detecting element exhibits a larger rate of thermal expansion at higher temperature. Thus, in the above described arrangement, since the stopper member is actuated in the stroking direction of the piston, the displacing amount of the stopper member is increased in direct proportion to the expansion amount of the temperature detecting element.
The stroke of the piston of known acceleration pumps generally falls within the range of between 3 to 5 mm. This stroke is too small to perform an accurate control of the acceleration fuel by the movement of the stopper member. In the worst case, the stopper member is displaced too largely, allowing no stroking of the stopper member.
Therefore, the acceleration pump combined with the incompressible temperature detecting element has not been used practically, in spite of its advantage to maintain a constant delivery rate from the acceleration pump against the fuel pressure.